This paper reports a qualitative investigation of factors contributing to success in 10 collaborative international forestry research projects funded by the Australian Centre for International Agricultural Research (ACIAR) in Vietnam. Success factors were identified, and the relative success of projects was evaluated in terms of research achievements and impacts, through analysis of ACIAR's project records and interviews with key project participants. This process identified 22 factors considered to either enhance or diminish project success, with the most frequently identified being: Collaborative scoping and design; skills mix and time allocations; funding and equipment; scientists' commitment and collaboration; and capacity building. Three projects, representing different categories of assessed research achievement and impact, were examined for evidence of relationships between these success factors and the relative success of the projects. This assessment suggested that most of the identified success factors were evident in the project with high research achievements and high impacts; and, conversely, that there was evidence of factors that diminish project success in a project that had low achievements and low impacts. The results reported here can help improve the design and implementation of future collaborative forestry research projects.